This invention relates generally to mounting apparatus and, more particularly, to a mounting bushing for mounting an overload protector within an opening in a structure, such as a motor shell.
Thermally actuated overload protectors are often provided in combination with small electric motors and similar devices to protect such devices from the effects of prolonged mechanical and electrical overloads, or other conditions which may lead to temperature increases and thermal overload of the subject devices. One example of an overload protector used for this purpose is the 2BM series, manual reset thermal protector which is manufactured by the KLIXON.RTM. subsidiary of Texas Instruments, Inc. The KLIXON.RTM. 2BM thermal protector is a normally closed device designed to protect fractional horsepower motors, while occupying a limited amount of space. The 2BM protector is typically mounted within the motor shell, in or immediately adjacent an opening in the shell which provides access to the manually actuated "pop-out" reset button.
Typical mounting arrangements for the KLIXON.RTM. 2BM thermal protector are described in Drawing No. EX 935-90 entitled "Mounting Variations for 2BM Motor Protector" which is available from Texas Instruments, Inc. of Attleboro, Mass. These arrangements include a variety of metal brackets which are typically attached by screws or other means to some portion of the mounting surface, and which support the 2BM protector against axial and rotational movement relative to the motor shell. Another mounting technique described in Drawing No. EX 935-90 involves the use of a circular spring clip. The 2BM protector has a cylindrical portion which surrounds the reset button and which is normally disposed within an opening (e.g., a round hole) formed in the mounting surface. A metal spring clip is forced over the cylindrical portion of the protector after that portion has been positioned within a round opening in the motor shell to secure the cylindrical portion of the protector to the shell.
Another mounting technique which is presently used by the assignee of the present application, and which involves the use of threads formed on the surface of the cylindrical portion of the 2BM protector, employs a washer and nut having an internal diameter which matches the external diameter of the threaded portion of the 2BM protector. When the protector is installed in this manner, the threaded cylindrical portion is aligned with and inserted through a round hole formed in the supporting structure. The metal washer and nut are placed over and threaded onto the cylindrical portion of the protector until a tight fit is obtained.
Although the above-discussed techniques for mounting the 2BM protector have been somewhat successful, certain disadvantages to these techniques have been noted. Each of the metal brackets described in Texas Instruments Drawing No. EX 935-90 must be attached by screws or other means to the inside of the mounting surface. This normally requires a manual assembly operation and requires handling and installation of screws, rivets or other fasteners. Use of the spring clip or washer and nut arrangements may reduce assembly time and the number of parts required. However, these techniques still require manual assembly and manipulation of two or more relatively small parts. Moreover, all of these mounting devices are formed of metal and, thus, present some shock hazard or risk of short circuit in the event of insulation breakdown or improper installation of the devices.
Another disadvantage of the mounting arrangements described above involves damage to the exposed portion of the thermal protector during the assembly, handling, or installation processes. When the thermal protector is mounted through an opening in the side of a motor shell, the reset button and a part of the cylindrical portion of the protector body extends through the opening and outwardly from the surface of the shell. As groups of motors are conveyed through the assembly process or gathered together for packaging or further processing, the exposed reset button and cylindrical portion may be struck by other motors or otherwise impacted in such a manner as to cause damage to the exposed protector or mounting device. In this event, the entire motor must be returned to the assembly area for repair and re-installation of a new thermal protector.
It is an object of the present invention to provide a novel arrangement for mounting a thermal protector which does not suffer from the disadvantages of prior art mounting arrangements.
Another object of the present invention is to provide a mounting arrangement for an overload protector which significantly reduces the material and labor costs associated with mounting the protector in a motor shell, as compared to Prior art mounting techniques.
Another object of the present invention is to provide a one-piece, non-metallic mounting bushing for an overload protector which may be employed to more quickly and easily mount the protector within an opening in a motor shell, and which improves the overall quality and reliability of the finished product.
Yet another object of the present invention is to provide a mounting bushing for an overload protector which provides a degree of mechanical protection for the exposed portion of the thermal protector after the protector has been mounting within an opening in a structure.
These and other objects of the present invention are attained in a bushing for mounting an overload protector within an opening in a motor shell, which comprises a plurality of segments adapted to be coaxially positioned around a portion of the overload protector, means formed on at least one of these segments for restricting movement of the overload protector relative to the segments, and means formed on the segments for securing the segments within the opening so as to restrict movement of the bushing and overload protector assembly relative to the motor shell. In one embodiment of the invention, the plurality of segments comprise a pair of generally symmetrical segments which are connected together by an integral hinge to form a unitary structure. This unitary structure is preferably molded in a single piece from a moldable thermoplastic material, such as nylon. In addition to being provided with features which restrict axial and rotational movements of the overload protector relative to the mounting bushing and motor shell, each of the segments is provided with a portion which extends outwardly from the exterior surface of the shell when the bushing is operably positioned within the opening so as to shield an otherwise exposed end portion of the overload protector from damage. These outwardly extending portions of the segments further comprise means for mounting a gasket to the bushing to protect the bushing and overload assembly from dust and other contaminants.
In one embodiment of the present invention, the bushing comprises a pair of generally symmetrical segments, each having an interior surface and an exterior surface. The interior surfaces of the segments define a cylindrical bore when the segments are in an opposing operable position. This bore is adapted to receive a mating cylindrical portion of the overload protector and to secure this portion of the protector against axial movements relative to the segments. Means are formed on the exterior surfaces of the segments for securing the bushing and protector assembly within the opening in the motor shell. Threads are provided on the interior surfaces of the segments which define the cylindrical bore, to mate with matching threads provided on an exterior surface of the cylindrical portion of the overload protector. These mating threads secure the overload protector against axial movements relative to the segments. Means are further provided on the exterior surface of at least one of the segments for restricting rotational movements of the overload protector relative to the bushing. In one particularly preferred embodiment of the invention, such means comprises a lip formed on the exterior surface of at least one of the segments. The lip extends in parallel relation to the common axis of the segments and protector. A portion of the lip is defined by a relatively flat surface which is positioned adjacent a flat surface of the overload protector when the segments are positioned around the protector so as to prevent rotational movement of the protector relative to the bushing segment. The means formed on the exterior surfaces of the segments for securing the segments within the opening preferably comprises a circumferential groove adapted to receive an edge portion of the motor shell which defines at least a portion of the opening in the shell. When the opening in the shell takes the form of a U-shaped slot, the circumferential groove receives a U-shaped edge portion of the shell which defines the slot. The bushing at the open end of the slot is secured in place by, for example, an end bell housing which is mounted to the end of the motor shell.
In an alternative embodiment of the invention, the interior surface of the cylindrical bore defined by the segments and the exterior surface of the cylindrical portion of the overload protector are smooth. In this embodiment, the means for securing the overload protector to the segments comprises a member extending from at least one of the segments across at least two surfaces of a rectangular portion of the overload protector. In this embodiment of the invention, the member comprises a first portion extending generally perpendicularly from the segment across a first surface of the protector, a second portion extending generally perpendicularly from the first portion across a second surface of the protector, and a third portion extending from the second portion across a third surface of the protector so as to secure the protector to the segment, and so as to prevent the protector from moving axially or rotationally relative to the bushing. The member thus at least partially surrounds the overload protector and holds the protector in position against opposing portions of the bushing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.